Hybrid charged-particle beam and light beam microscopy

ABSTRACT

A charged-particle beam microscope is provided for imaging a sample. The microscope has a stage to hold a sample and a charged-particle beam column to direct a charged-particle beam onto the sample. The charged-particle beam column includes a charged-particle beam source to generate a charged-particle beam, and charged-particle beam optics to converge the charged-particle beam onto the sample. The microscope also has a light beam column to direct a light beam onto the sample. The light beam column includes a light beam source to generate a light beam, and light-beam optics to converge the light beam onto the sample. One or more detectors are provided to detect charged-particle and light radiation emanating from the sample to generate an image. A controller to analyze the detected charged-particle radiation and detected light radiation to generate an image of the sample.

CLAIM FOR PRIORITY

This application claims priority under 35 U.S.C. §119(e) to ProvisionalApplication 62/013,514, filed Jun. 17, 2014, and U.S. patent applicationSer. No. 14/607,079, filed Jan. 28, 2015, which claims priority under 35U.S.C. §119(e) to Provisional Application No. 61/932,159, filed Jan. 27,2014, all of which are incorporated herein by reference in theirentireties.

TECHNICAL FIELD

This application relates to improvements in microscopy.

BACKGROUND

Microscopy, which includes charged-particle beam microscopy and lightmicroscopy, can be used to image samples at very small dimensions. Forexample, charged-particle beam microscopy, which includes electronmicroscopy and focused ion beam microscopy, can be used to investigatesamples at dimensions smaller than what is possible using solely lightmicroscopy. Charged-particle beam microscopy may also reveal informationthat is not readily available through light microscopy, such as inrelation to composition, crystallography, and topography of the sample.

However, conventional charged-particle microscopes typically have anumber of practical disadvantages compared to light microscopes.Conventional charged-particle microscopes are usually cumbersome tomaintain and repair. For example, replacing worn or damaged internalcomponents of a microscope may require specialized knowledge and extremecare so as not to contaminate the normally evacuated space within themicroscope or damage the sensitive componentry.

Moreover, microscopes may be complicated to operate, requiring extensivetraining. In addition, microscopes may be expensive and require thehuman operator who wants to image a sample to be present at themicroscope or at a single user terminal that is locally connected to themicroscope. Popular access to the benefits of certain types ofmicroscopy has therefore been severely limited.

Thus, it is desirable to provide microscopy that is reliable and permitsrelatively easy maintenance and repair. It is also desirable for amicroscope to be relatively accessible and easy to use without extensivetraining.

SUMMARY

In one embodiment, a charged-particle beam microscope is provided forimaging a sample. The microscope comprises a stage to hold a sample anda charged-particle beam column to direct a charged-particle beam ontothe sample. The charged-particle beam column comprises acharged-particle beam source to generate a charged-particle beam, andcharged-particle beam optics to converge the charged-particle beam ontothe sample. A light beam column is provided to direct a light beam ontothe sample. The light beam column comprises a light beam source togenerate a light beam, and light-beam optics to converge the light beamonto the sample. A detector is provided to detect both charged-particleand light radiation emanating from the sample to generate an image. Acontroller analyzes the detected charged-particle radiation and lightradiation to generate an image of the sample.

In another embodiment, a charged-particle beam microscope is providedfor imaging a sample. The microscope comprises a stage to hold a sampleand a charged-particle beam column to direct a charged-particle beamonto the sample. The charged-particle beam column comprises acharged-particle beam source to generate a charged-particle beam, andcharged-particle beam optics to converge the charged-particle beam ontothe sample. A first detector is provided to detect charged-particleradiation emanating from the sample to generate an image. The microscopefurther comprises a light beam column to direct a light beam onto thesample. The light beam column comprises a light beam source to generatea light beam, and light-beam optics to converge the light beam onto thesample. A second detector is provided to detect light emanating from thesample to generate a second image. A controller analyzes the detectedcharged-particle radiation and the detected light to generate an imageof the sample.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate several embodiments and aspectsof the transmission electron microscopes described herein and, togetherwith the description, serve to explain the principles of the invention.

FIG. 1 is a schematic diagram of an example of an embodiment of ascanning electron microscope (SEM).

FIGS. 2A, 2B, and 2C are schematic diagrams of an example of anembodiment of a stage mechanism for a microscope.

FIGS. 3A and 3B are three-dimensional rendered perspective views of theexample of the embodiment of stage mechanism illustrated in FIGS. 2A,2B, and 2C.

FIGS. 4A, 4B, 4C, and 4D are schematic diagrams of examples ofembodiments of detectors arranged on mounted platforms.

FIG. 5 is a schematic diagram of an exemplary embodiment of a scanningtransmission electron microscope (STEM).

FIG. 6 is a schematic side view of an example of an embodiment of anoptical column for a charged-particle beam microscope.

FIG. 7A is a schematic side view of an example of an embodiment of amodular microscope.

FIG. 7B is a schematic diagram of a top view of an accessory mount of amodular microscope.

FIG. 7C is a schematic side view of an example of an embodiment of acolumn module inserted in a column mount of a modular microscope.

FIG. 8A is a schematic top view of a multi-accessory printed circuitboard (PCB).

FIG. 8B is a cross-sectional side view of Section A-A shown in FIG. 8A.

FIG. 8C is a schematic top view of one of the regular-type connectorsshown in FIG. 8A.

FIG. 9A is a schematic perspective view of the PCB shown in FIG. 8A.

FIG. 9B is a three-dimensional rendered perspective view of the PCBshown in FIG. 9A.

FIG. 10A is a schematic side view of an example of an embodiment of acompact evaporator.

FIG. 10B is a schematic side view of an embodiment in which a compactevaporator is located inside the chamber of a microscope.

FIG. 11A is a schematic side view of an example of an embodiment of aprotective screen module in a microscope to protect the microscope froma process occurring near the sample.

FIG. 11B is a schematic top view of an example of an embodiment of aprotective screen module.

FIG. 12A is a schematic side view of an example of an embodiment of ahybrid SLM-SEM.

FIG. 12B is a schematic side view of an example of another embodiment ofa hybrid SLM-SEM.

FIG. 12C is a schematic side view of an example of an embodiment of alaser module of a scanning light module.

FIG. 12D is a schematic side view of an example of an embodiment ofrespective fields of view of a scanning light module and acharged-particle beam microscope.

FIG. 13A is a schematic diagram of a light beam passing through asample.

FIG. 13B is a schematic diagram of a light beam being scanned across asample.

FIG. 14A is an electrical schematic diagram of an example of a firstembodiment of two-battery bank power supply.

FIG. 14B is an electrical schematic diagram of an example of a secondembodiment of two-battery bank power supply.

FIG. 15 is a schematic diagram of an example of an embodiment of asystem for electrically-isolated wireless communications between a userinterface (UI) and a microscope.

DETAILED DESCRIPTION

A microscope—such as a charged-particle beam microscope, lightmicroscope, atomic force microscope, or scanning tunnelingmicroscope—may be adapted and used advantageously to image and examinesamples. A charged-particle beam microscope may be, for example, anelectron microscope (EM) or focused ion beam (FIB) microscope. An EM maycomprise, for example, a scanning electron microscope (SEM), scanningtransmission electron microscope (STEM), or transmission electronmicroscope (TEM). The microscope may illuminate the sample with one ormore beams (such as charged-particle beams or light beams) and detectradiation from the sample to generate an image of the sample. A SEM orSTEM, for example, scans an electron beam that is formed into a probeacross the sample. A light microscope may be, in one version, a confocalmicroscope that illuminates the sample with a light beam and observesreflected light. One example of a confocal microscope is described inU.S. Pat. No. 5,161,053 to Dabbs, which is incorporated herein byreference in its entirety. The images may be evaluated, such as by ahuman user of the microscope, to identify characteristics of the sample.

FIG. 1 is a schematic diagram of an example of an embodiment of amicroscope 10 that is a SEM 10A, provided for the sake of illustration.SEM 10A has a housing that, when closed, is substantially airtight anddefines a chamber with an enclosed volume therein. A sample 20 can beplaced inside SEM 10A, such that an area that can be exposed to anelectron beam probe 30 for imaging. Sample 20 may include and besupported, for example, by a substrate (not shown). Sample 20 may be ofany quantity, may be of any suitable shape or size, and may include anydesired features. For example, sample 20 may include a specificconfiguration for a desired application or parameter setting. In anotherembodiment, discussed in further detail below, sample 20 is a reference(or “test”) sample used for testing or optimization purposes, such ascontaining gold nano-particles. The substrate that can be used tosupport sample 20 may include a layer of crystalline or amorphouscarbon. Single-atomic-layer graphene may also be used. Alternatively orin addition, the substrate may include boron nitride, silicon, silicondioxide, aluminum, polymeric resins, or organic materials.

SEM 10A may have a stage 40 to support and move sample 20 within SEM10A. In one version, stage 40 is adapted to be moved continuously whilethe charged-particle beam is simultaneously scanned. This may improvethroughput by allowing continuous acquisition of images whileeliminating the settling time caused by stop-start motion of a stagethat is moved discretely and that may prevent acquisition of a stillimage of the sample.

For example, stage 40 may be a piezoelectric stage. The piezoelectricstage may have a piezoelectric motor that is capable of moving the stagevery quickly and smoothly so that short exposures on the order ofmilliseconds or microseconds can be practically achieved. Thepiezoelectric stage may also be adapted to move the stage with very highpositional precision. In one embodiment, the stage motor is capable ofdisplacing the sample at a speed of at least about 100 nm per second.

In one version, a stage mechanism is provided that includes an arcedtray adapted to rotate about a hinge with stage 40. Previously describedstage 40, including motors to move stage 40, may be mounted in the trayof this stage mechanism. FIGS. 2A, 2B, and 2C are schematic diagrams ofan example of an embodiment of such a stage mechanism 50—a toptransparent view in which tray 60 is closed, a top transparent view inwhich tray 60 is open, and a front view in which tray 60 is closed,respectively. FIGS. 3A and 3B are three-dimensional rendered perspectiveviews of this example of the embodiment of stage mechanism 50, with tray60 in closed and opened states, respectively.

This version of stage mechanism 50 may provide several advantages overconventional microscope stages, which typically have a tray mounted on alinear roller. First, the rotating mechanism of this version enableseasy access to stage 40 for loading and unloading. Rotating tray 60, asit is being opened, moves a door 70 out of the way of the user,presenting the unobstructed side of stage 40 to the user and therebyenabling easy access to sample 20 on stage 40. Unlike some conventionaldoor mechanisms, door 70 does not squarely face the user and therebyobscure visibility of sample 20. The height of sample 20 can also beobserved easily during opening and closing of door 70, reducing thechances that the user's valuable sample 20 is damaged by impact ofsample 20 against sample chamber opening 80. A collision with sample 20could not only damage user's valuable sample 20, but it could alsocontaminate a seal 90 on sample chamber 100 around chamber opening 80and contaminate the column with fractured pieces of sample 20. In thisembodiment, however, stage mechanism 50 provides increased visibility ofsample 20 by the user.

Second, relatively few mechanical parts may be needed to efficientlytransition stage 40 between sample chamber 100 and the outsideenvironment. The rotary motion of tray 60 can permit less lineardisplacement of sample 20 than the concurrent displacement of handle 110of tray 60 when tray 60 is being opened or closed. This may permit theuser greater sensitivity in observing and manipulating the position ofsample as door 70 is being opened or closed. Moreover, a hinge 120 canbe equipped with easy-to-machine cylindrical parts that enable dampingand predefined resting positions of door 70 in open, closed, andin-between states, respectively. This also contributes to a sensitivetreatment of sample 20.

Third, stage mechanism 50 may have greater reliability than conventionalmethods and systems for inserting samples into and removing samples fromstage 40. Interconnections to and from stage 40, such as wiringharnesses, are subject to rotational stresses, which can result ingreater lifetime than linear stresses. Furthermore, hinges 120 may bemore compact and less sensitive to dust and particles than linear rails.

Fourth, stage mechanism 50 may provide easy accessibility and servicingof stage 40. For example, stage 40 can be a drop-in module that israpidly exchanged or repaired without opening the microscope housing.Once closed, strategically placed dampers, such as damper 130 shown inFIGS. 2A and 2B, may be placed in kinematic contact with tray 60, suchas by attachment to tray 60. This, combined with seal 90 and hinge 120,which can both be configured with damping properties, can serve tostabilize tray 60 to substantially remove mechanical instability inorder to permit stable imaging by microscope 10 at high resolution.

In addition, stage mechanism 50 may be communicatively coupled to acontroller of microscope 10. For example, a door closure sensor 140,which may be placed internally or on the face of door 70, mayautomatically notify the controller of microscope 10 when door 70 hasbeen closed and microscope 10 is ready to pump down to vacuum. Inanother embodiment, the door closure sensor 140 is integrated withhandle 110, which may be configured with a ready switch to notify thecontroller of readiness for pumpdown. Handle 110 may be configured totoggle or rotate to deliver on or off signal states.

Returning to FIG. 1, SEM 10A further includes an electron beam source 35to generate an electron beam 150. Electron beam source 35 may be adaptedto generate an electron beam having a current of less than about 100 mA.For example, for many applications electron beam source 35 may generatea beam current of from about 10 picoamps to about 1 milliamp. In anespecially low-current version, however, electron beam source 35 may beadapted to generate electron beam 150 to have a current of less thanabout 10 μA, such as less than about 10 pA. Electron beam source 35 mayhave a filament (e.g., tungsten filament) through which current ispassed to generate electrons and a Wehnelt to channel the electrons intoa beam. Further, electron beam source 35 may have an acceleratingaperture to accelerate the electron beam away from electron beam source35.

SEM 10A has an optical system through which electron beam 150 travelsfrom source 35 to sample 20, and optionally through which electron beam150 travels after it has been transmitted through sample 20. The opticalsystem may define an optic axis 160 along which electron beam 150travels. The optical system may include illumination optics. Theillumination optics may include condenser lenses 170A-C to form electronbeam 150 into a collimated probe 30 that illuminates sample 20.Condenser lenses 170A-C may consist of, for example, two, three (asshown in the figure), or four lenses. Condenser lenses 170A-C may bemagnetic or electrostatic.

The optical system of SEM 10A may also include an objective lens 180 tofocus electron beam 150. An objective aperture may be provided in theback focal plane of objective lens 100 or a plane conjugate to the backfocal plane to define an acceptance angle, referring to an angle ofelectron beam 150 that is transmitted through the aperture and allowedto illuminate sample 20. The rays that objective lens 100 focuses toprobe 30 on sample 20 are thus limited in angle by the aperture.

One or more beam scanners 190 may be provided to scan electron beam 150across sample 20. FIG. 1 shows an example of a scanned beam 200 at asecond position. Beam scanners 190 may scan electron beam 150 bygenerating either a magnetic or an electric field. For example, beamscanners 190 may include scan coils that generate an alternatingmagnetic field. Alternatively, beam scanners 190 may use electrostaticdeflectors to scan electron beam 150. Beam scanners 190 may be providedin pairs, such as two or four paired electromagnetic coils orelectrostatic deflectors. Beam scanners 190 can be excited with rampwaveforms, causing the collimated probe to be scanned across the sampleand thereby producing an intensity signal at the detector unique to thelocation of the probe on the sample. FIG. 1 shows an example of electronbeam 150 being scanned between a first position and a second position200.

In one version, beam scanners 190 are adapted to provide a larger fieldof view compared to conventional charged-particle beam microscopes. Forexample, beam scanners 190 may include double-rocking scan coils, coilswith a greater turns ratio, or higher-power (i.e., higher-current) scancoils. Alternatively or in addition to scan coils, beam scanners 190 mayinclude electrostatic deflectors that can slew greater voltages, such asvoltages greater than about 15 V. These embodiments can increase thesize of the field of view of the microscope. Large field-of-view beamscanners such as those described above may advantageously be used incombination with a long-working-distance optical column to enhance theefficacy of the optical column by enabling larger areas to be surveyedin one image without translation of the sample or multiple images beingtaken and later montaged.

When sample 20 is illuminated by electron beam 150, electrons interactwith sample 20, producing radiation that emerges from the sample surfacein a pattern that is collected by one or more detectors 210A, 210B.Detectors 210A, 210B may detect radiation that can include one or moreof backscattered electrons, secondary electrons, auger electrons,cathodoluminescence, ionized gas, and x-rays, and generate acorresponding signal.

The electron-beam energy used in SEM 10A may be selected at least inpart based on the target resolution, the transmission properties ofsample 20, and the energy of the detected radiation. The penetrationdepth of the beam into sample 20 may be selected to permit the escapeand detection of interaction radiation from sample 20. The penetrationdepth may be selected to be, for example, from about 1 nanometer toseveral micrometers, such as, for example, a penetration depth on theorder of 2 nanometers, to result in a range of sensitivities to surfaceor subsurface structure.

If electrons of electron beam are reflected or deflected from sample 20,they are considered scattered. For example, electrons scattered backtoward the electron-beam source are referred to as backscattered. In oneexample, backscattered electrons can be successfully detected if theyhave an energy of at least about 2 keV. As a result, electrons having anenergy of from about 2 keV to about 3 keV may have the lowest beamenergy appropriate to permit detection of backscatter electrons in thisexample, unless a backscatter detector of low-energy type is used, inwhich case backscattered electrons with energies of less than about 1keV may be detected. Secondary electrons, on the other hand, areproduced by secondary processes at sample 20 and may possess far lowerenergies of, for example, from a few Volts to a few hundred Volts. Thus,the detection of secondary electrons may be compatible with lower beamenergies. Lower beam energies have advantages in certain problem spaces,which may include being less destructive to samples, less deeplypenetrating (i.e., more surface-sensitive), and requiring lower-costequipment to generate and stabilize the accelerating potential.

Detectors 210A, 210B may detect charged particles, such as scatteredelectron beams, emerging from sample 20 at one or more angles. Each ofdetectors 210A, 210B may comprise, for example, a scintillator and aphotosensitive detector. The photosensitive detector may be, forexample, a charge-coupled device (CCD). The scintillator producesphotons when impacted by charged particles. The photosensitive detectorreceives that light and outputs a corresponding electrical signal.

The intensity and/or angle of scattered electrons may vary according tothe atomic number (Z) of atoms in sample 20. For example, a greaternumber of electrons may be backscattered and produce a higher-intensitysignal at detectors 210A, 210B when atoms of higher atomic number areilluminated. In one embodiment, atoms of sample 20 having higher atomicnumber scatter electrons to higher angles, while lighter atoms scatterelectrons to lower angles, revealing information about the compositionof sample 20.

Detectors that are photosensitive may be provided to detectlight-emitting phenomena such as cathodoluminescence or fluorescence.These may be the same detectors as or different detectors than thecharged-particle-sensitive detectors such as detectors 210A, 210B. Forexample, a charged-particle-sensitive detector that is made of ascintillator and a photosensitive detector may have a scintillator thatis substantially optically transparent, such that photons pass throughthe scintillator and are detected by the same photosensitive detector.

A photosensitive detector of microscope 10 may even be adapted to besensitive to particular preselected wavelengths. For example, an arrayof multiple detectors with varying spectral sensitivity may be provided.Photons within a tight spectral window may be detected by a siliconphotomultiplier (SiPM) that amplifies their signal into an electricalsignal. Alternatively, a multi-spectrum or broad spectrum SiPM maydetect these photons such that photons of multiple preselectedwavelengths within a wider range may be detected simultaneously.

In one version, charged-particle-sensitive detectors are configured inone or more concentric annular rings and a central circular discdetector in an approximately cylindrically symmetric detectorarrangement to receive the electrons (as shown in FIG. 1). There may beapertures between detectors 210A, 210B. For each range of angles,detectors 210A, 210B may provide an intensity signal corresponding tocurrent received for that angular range. If the detector is a CCD, thescattered beams may form an image of a diffraction pattern or channelingpattern of sample 20.

Alternatively to concentric, on-axis detectors, the detectors may have ashape that is cylindrically asymmetric. For example, the detectors maybe segmented or configured as area detectors that are arranged off-axis.In other embodiments, the detectors have an inner or outer perimeterthat is polygonal, such as square or hexagonal, or another suitableshape.

In one version, a detector-shifting mechanism is provided to move one ormore of the detectors in situ during acquisition of an image or betweenacquisitions of images. The mechanism may have detector mounted on itand may have an actuator that moves the detector in response to an inputsignal. This may enable selective detection of the backscatter signal inazimuthal or radial dimensions, for example. By varying detectorposition, the apparent direction of the “light” source of the image iscontrolled. Additionally, the angle of detected backscatter signal,which may have an intensity distribution that is a function of atomicnumber in the sample, may be controlled.

In one embodiment, a miniature detector, for example a siliconphotomultiplier (SiPM), is mounted on a rotating platform. FIG. 4A is aschematic diagram of an example of this embodiment. A mechanical mount220 holds a rotating platform 230, such as by an arm 240 between them.Rotating platform 230 supports at least one detector 190A. This permitsselective detection of the backscatter signal azimuthally. Rotatingplatform 230 may have an opening 250 in its center to allow transmissionof beam 150 therethrough. FIG. 4B is a schematic diagram of a side viewof detector 210A and beam 150.

FIG. 4C is a schematic diagram of another example of this embodiment. Inthis example, an array of multiple detectors 210A is mounted in asubstantially circularly symmetric pattern on platform 230. Platform 230may have opening 250 in its center to allow transmission of beam 150therethrough.

In another embodiment, detectors may be arranged in a substantiallycircularly asymmetric pattern. FIG. 4D is a schematic diagram of anexample of such an embodiment. In this example, detectors 210A arearranged in an arc pattern. Platform 230 may have opening 250 at thebeam axis to allow transmission of beam 150 therethrough. Mechanicalmount 220 may have a telescoping arm 240 that can move platform 230toward or away from mount 220, such as by another, separately controlledactuator.

SEM 10A may be adapted to operate in a “low-angle” backscatter mode inwhich a detector, such as detector 190B, detects a “low-angle-scattered”electrons emerging from specimen 20. This low-angle mode may beparticularly sensitive to light elements in the sample, differentiatingfrom heavier elements and indicating chemical composition.

Alternatively to the low-angle backscatter mode, SEM 10A may be adaptedto operate in a high-angle backscatter mode in which one or moreelectron beams emerging from sample 20 within a particular angular rangeare detected. Since sample 20 is illuminated at approximately a point,this angular range of detection can be tightly controlled. For example,the high-angle backscatter mode may be a high-angle mode in which anelectron beam shaped as a hollow cone of preselected thickness isdetected. The high-angle backscatter mode may involve detecting a hollowcone at higher angles, which is referred to as high-angle backscattermode. The dark-field mode may also be a medium-angle backscatter mode,in which a range of angles between the low-angle mode and high-anglemode are detected. These dark-field modes can produce an image withmonotonic contrast change with increasing atomic number, which enablesdirect interpretability of the image to determine relative atomicweights. For example, high-angle backscatter imaging can be used toobtain chemically sensitive images of clusters of molecules, atoms, ornanostructures. An electron beam source having a high-brightness gun mayallow this mode to operate faster.

Additional signals, such as secondary electrons and x-rays produced bythe interaction between electron probe 30 and sample 20, may also besimultaneously detected in the region near the sample by one or moredetectors, such as a detector 210E.

FIG. 5 is a schematic diagram of another exemplary embodiment ofmicroscope 10, which in this case is a STEM 10B, provided for the sakeof illustration. In the STEM mode, the scattered beam is at leastpartially transmitted through sample 20 and this portion is thereforeconsidered forward scattered. STEM 10B, like SEM 10A, may have a stage(not shown), electron beam source 35, illumination optics 170A, 170B,170C, aperture 260, objective lens 100, beam scanners 190, and detectors210A-C, 210E.

In order to improve speed, accuracy, and sensitivity, STEM 10B may havea dedicated aberration corrector 270 to correct for aberrations inelectron beam 150, such as spherical aberrations and parasiticaberrations. The parasitic aberrations may or may not be cylindricallysymmetric. Aberration corrector 270 may include electromagnetic lensesto correct for these aberrations. Parasitic aberrations may be caused,for example, by the optical elements having been machined in such a wayas to be very slightly off-axis or very slightly non-round. Examples ofcommercially available aberration correctors include Nion Co.quadrupole-octupole correctors (available from Nion Company of Kirkland,Wash.) and CEOS sextupole or quadrupole-octupole correctors (availablefrom Corrected Electron Optical Systems GmbH of Heidelberg, Germany).

The optical system of STEM 10B may also include descanning andprojection optics 280. The descanning optics may de-scan scatteredelectron beams 290A, 290B, thus, for example, realigning beam 290B withoptic axis 160. The descanning optics may comprise, for example,descanning coils that may be symmetric to scan coils of beam scanners190. The projection optics may include magnifying lenses that allowadditional manipulation of scattered electron beams 290A, 290B.

The electron beam energy used in STEM 10B may be determined at least inpart based on the transmission properties of sample 20. A substrate ofsample 20 may have a thickness on the order of 2 nanometers, such as forexample a thickness of about 1 nanometer. In one example, the substrateis made of carbon, although single-atomic-layer graphene may also beused. As a result, 1 keV electrons may be the lowest energy appropriatewhen considering voltage alone.

STEM 10B may be adapted to operate in a “bright field” mode in which adetector, such as detector 210C, detects a “forward-scattered” or“central” beam 290B of electrons emerging from specimen 20.Forward-scattered beam 290B refers to the zero beam (i.e., the 0scattering vector, referring to the beam whose direction is identical tothe orientation of beam 150 impinging on specimen 20) and a small rangeof angles around the zero beam. The bright-field mode may beparticularly sensitive to the energy loss of the electrons, indicatingchemical composition. These electrons can be detected to determine, forexample, bonding energies of molecules that compose the sample.

Alternative to the bright-field mode, STEM 10B may be adapted to operatein a dark-field mode in which one or more electron beams 290A emergingfrom sample 20 within a particular angular range are detected. Sincesample 20 is illuminated at approximately a point, this angular range ofdetection can be tightly controlled. For example, the dark-field modemay be an annular-dark-field (ADF) mode in which an electron beam shapedas a hollow cone of preselected thickness is detected. The dark-fieldmode may involve detecting a hollow cone at higher angles, which isreferred to as high-angle annular-dark-field (HAADF) mode. Thedark-field mode may also be a medium-angle dark-field (MADF) mode, inwhich a range of angles between the bright-field mode and the HAADF modeare detected. These dark-field modes can produce an image with monotoniccontrast change with increasing atomic number, which enables directinterpretability of the image to determine relative atomic weights. Forexample, dark-field imaging can be used to obtain chemically sensitiveprojections of single atoms, clusters of atoms, or nanostructures. STEM10B can also operate in simultaneous bright-field and dark-field modes.An electron beam source having a high-brightness gun may allow this modeto operate faster.

In one version, STEM 10B may have a detector 210D adapted to detectelectrons in one or more preselected range of energies. Coupling optics300 may be provided and detector 210D may include an electron prism 310to filter out electrons that are not in the preselected energy ranges.In one version, this is used for electron energy loss spectroscopy(EELS). Electron prism 310 may, for example, generate an electric ormagnetic field by using electrostatic or magnetic means, respectively.The field strength and dimensions of electron prism 310 may be selectedsuch that, when the electrons of varying energies pass through thefield, the electrons in the preselected energy range are transmittedthrough electron prism 310 while the remaining electrons are blocked.Detector 210D may also include a receiver 320, such as including ascintillator and CCD, to receive the transmitted electrons and convertthat current into a detection signal. The EELS detection signal can beexpressed as a plot 330 of current as a function of electron energyloss.

Furthermore, optics having a larger acceptance angle may improveresolution of STEM 10B. Because of this relationship between theacceptance angle and resolution of STEM 10B, the acceptance angle can beselected based on the desired resolution. For example, in ahigh-resolution STEM, if 1 Angstrom resolution at 100 kilovolts isdesired, it may be desirable to have at least about 30 milliradiansacceptance half-angle, or even at least about 40 milliradians acceptancehalf-angle. However, with an angular range that is unnecessarily high,current may be wasted undesirably. Once a suitable accelerating voltageis chosen, the desired resolution may determine the acceptance angle ofobjective lens 180.

Moreover, detectors 210A-E from SEM and STEM embodiments, such as, forexample, from FIGS. 1 and 5, respectively, may be provided concurrentlyin one embodiment of microscope 10. These may be provided, for example,to operate microscope 10 in simultaneous SEM and STEM modes or to allowrelatively quick and easy switching between SEM and STEM modes.

The geometry of one or more of detectors 210A-C may be adapted todistinguish low-angle scattering from high-angle scattering in bothforward and backscattering configurations to make contrast in the imagedepend on atomic number (Z). Detectors 210A-C may be located on the sameside of sample 20 as electron beam source 35 or opposite to it. Forexample, in a STEM mode, detector 210A may be provided to operate in aHAADF mode in which high-angle electron beam 210A is detected, detector210B may operate in a MADF mode, and detector 210C may operate in abright-field mode in which axial electron beam 210B including a zerobeam is detected.

Each of detectors 210A, 210B, if arranged in a substantiallycylindrically symmetric geometry, may limit the scattered electrons toan angular range denoted here as φ_(d), which defines an annulus betweenan inner angle φ₁ and outer angle φ₂. For an ADF mode these angles maybe, for example, from about 25 mrad to about 60 mrad for φ₁, and fromabout 60 mrad to about 80 mrad for φ₂. For a STEM HAADF mode usingdetector 210A, these angles may be, for example, from about 60 mrad toabout 80 mrad for φ₁, and greater than about 100 mrad for φ₂.

The optical system of a beam-optical microscope (i.e., charged-particlebeam microscope or light microscope) may be referred to as the optical“column.” FIG. 6 is a schematic side view of another example of anembodiment of an optical column 340 for a charged-particle beammicroscope. If scanning coils are included, optical column 340 may bethe optical column of, for example, a scanning electron microscope(SEM). Alternatively, optical column 340 may be used on the source sideof a transmission electron microscope (TEM).

This column 340 includes a charged-particle beam source 35 (e.g.,electron or ion beam source), which has a gun 350 that provides chargedparticles at a predefined voltage. The voltage may be in the range offrom about 1 kV to about 100 kV, with polarity as needed to propel theions down the column. Source 35 may include a centering mechanism 360,such as, for example, adjustable screws or a motor that is eithermanually or computer controlled. Source 35 may also have a Wehnelt 370to provide focusing of the particles as they leave the source. Wehnelt370 may be set at a voltage close to the particle source voltage andeither attractive or repulsive to the particles. For example, thevoltage may be set in the range of from about −10 V to about −1000 V andrepellant to the charged particles. Source 35 may be surrounded by aninsulator 380.

Column 340 may also include a first anode 390, which may be held atground or other voltage more positive than the beam source 35, to whichthe particles are attracted. First anode 390 may have a hole in itscenter (or elsewhere) through which a portion of the charged particlespasses. Further downstream, column 340 may also include a number ofcondenser lenses 170A, 170B or other electron-optical elements to adjustthe beam before objective lens (OL) 180. These may be configured in anysuitable order or combination. Column 340 may also have stigmators 400.There may also be a final aperture (objective aperture) 410 before OL180. Finally there is OL 180, followed by sample 20.

Optionally there may be additional components between OL 180 and sample20, such as stigmators or electrical shifters. The column design in thisexample is adapted for simplicity. For example, the lenses may not bealignable and there is only one aperture (i.e., the objective aperture)in the whole column (although the bores of condenser lenses 170A, 170Bmay act to obstruct some of the beam).

The charged-particle optical column may have individual lenses withinterconnections at each lens, such as for power, water cooling, and/orsensing. However, such a column may be relatively difficult andexpensive to manufacture, align, and service. For example, each lens mayhave to be independently aligned to its neighboring lenses and the axisof the column. If there is a malfunction, the electrical connections inthe stack of components of the column that are above the malfunction andpotentially others below it may have to be disconnected and the entireoptical column opened up in order to provide service.

Thus, it may be advantageous to integrate a number of, or all of, theoptical components, electrical contacts, and vacuum couplings of theoptical column into a monolithic column that is designed to remain as anintegrated unit rather than to be capable of being disassembled intoparts. The monolithic column may also be manufactured relativelyinexpensively. For example, layers of the monolith may be stacked orfabricated as a single piece and then the monolith may be machined as aunit to fabricate the monolithic column. The monolithic column may besubstantially shaped as, for example, a compact tube. Alternatively, themonolithic column may be shaped to provide advantageous connection ofoptical components, electrical contacts, or vacuum couplings.

Such a monolithic column may provide a number of advantages compared toother columns. First, the interconnections may be provided in arelatively simple configuration and the number of interconnections canbe reduced. In one example, all signal communications between themonolithic column and the rest of the microscope may be provided througha single interconnection at a mechanical mounting point of themonolithic column at which the column is mounted to the housing of themicroscope.

The monolithic column may also be able to be manufactured relativelyinexpensively. Thus, the monolithic column can be adapted to be replacedeasily, such that a failure of the column due to, for example,contamination of the optics in the column, component failure, or expiryof consumable parts such as a filament, can be addressed efficiently andrelatively inexpensively.

The optical components within the monolithic column may be designed tohave low drift (both mechanically and electrically). This can permit thecolumn to be stored and operated in a wide variety of temperatures andconditions. This is achievable using low temperature coefficientmaterials, or making use of combination materials, and/or specialgeometries that take advantage of symmetries with error-cancelingproperties to compensate for the effects of thermal expansion.

The mechanical spacing of the optics in conjunction with fixed lenssettings enables monolithic columns to have purpose-built illuminationmodes (and also projector modes in TEM). Variations of the monolithiccolumn can provide different working distances or illuminations, forexample high current or high resolution illumination modes in a singlelow-cost column that is easily switched out.

In the case of electrostatic optics being used in the monolithic column,a single supply can be used to define both the accelerating potential aswell as other potentials such as lens potentials by means of dividers,thereby enabling a fixed-focus or limited-focus microscope column thathas very few parts end-to-end, using only a single power supply and verysimple mechanical construction.

Electrostatic optical components may enhance imaging or observation ofmagnetic samples. This is in addition to the advantage of being able touse a single supply to power all lens elements. Trim lenses may be usedfor as “fine” focusing to modify the “coarse” focus of the primarylenses such as the objective lens. The coarse focus lens may have afixed focus. Alternatively, the column may be operated as a fixed-focuslens, where focusing is performed by altering the position of the samplerelative to the optical components of the column.

An electrostatic trim lens can also be used within the system to providefine focusing. Because it offers trim, it may be operated at one to twoorders of magnitude lower potential than the primary lens potentials.This trim lens may take the form of a single aperture with a potentialapplied, or may be a more formal lens such as a full Einzel lens that isweakly excited.

A variation of the above-described embodiment uses one or more magneticlenses. In practice, magnetic lenses may have from about two to aboutthree times lower spherical aberration and about five times lowerchromatic aberration than electrostatic lenses, so increased resolutioncan be obtainable by using a magnetic lens instead of an electrostaticlens. Similarly, this could be done with one more of the condenserlenses, as the chromatic aberration is additive throughout the system. Apotential drawback of using magnetic lenses, however, despitepotentially increased resolution, is increased bulk, power consumption,and corresponding heat dissipation. Nevertheless, the size and strengthof such a magnetic lens may be adjusted to substantially balance outthese effects.

For example, a fixed magnetic objective lens may be provided.Furthermore, a magnetic trim lens may be provided to adjust the focus ofthe objective lens. The magnetic trim lens can operate with low voltagesand low excitations to conserve power while providing fine focusingcapability.

The optical column may be constructed as a module that is enclosed andadapted to be inserted and locked into the microscope enclosure andremoved therefrom by a human user. The microscope housing maycomplementarily be adapted to receive the column module. Both the columnmodule and the microscope housing may be adapted to permit signalcommunication between the column module and other components of themicroscope when the column module is locked into the microscope.

The column module may contain components of a charged-particle opticalcolumn, such as but not limited to the charged-particle beam source.Optical elements, such as lenses, shape the beam as it propagatesthrough the column. The components may also include, for example, anaccelerating aperture (such as a first anode), a stigmator, beamscanners to scan the beam, and detectors. Sidewalls of the enclosure maybe made of an electrical insulator in one embodiment. The top of theenclosure, meanwhile, may be metal.

The column module may be substantially sealed from an environmentexternal to the column. For example, when evacuated, the column modulemay maintain a significant pressure difference between the volume insidethe column module and the external environment. The internal volume andthe external environment may even have different species of gases orliquid.

The column module may have a feedthrough that allows electrical signalsto be conducted through enclosure and into the column module, such thatsignals may be applied to the components inside the column module. Forexample, electric potentials may be applied, through the feedthrough,independently to the gun of the charged-particle beam source and theoptical components. The feedthrough may have electrical leads withexposed electrical contacts that couple to electrical contacts of themicroscope housing when the column module is inserted and locked intomicroscope 10. As an alternative to electrical signals, the feedthroughmay be adapted to convey optical signals, such as through optical fibersembedded in the feedthrough.

It may therefore be advantageous to separate the volumes using variousvolume separators. For example, the volume separator may be a suitablythin beam-transmission membrane. A thin gas-impermeable membrane may besubstantially transparent to the charged particle beam, whilemaintaining the difference in pressure and substantially eliminating thegas jet.

The column module may have an emission window positioned after the finalcomponent contained within the volume inside enclosure. The emissionwindow may be substantially opaque to gas particles while simultaneouslybeing substantially transparent to the accelerated particles. To achievethese properties, emission window may be fabricated to be very thinwhile having high strength. For example, the emission window may befabricated of silicon nitride (SiN). The portion of the emission windowthat is substantially transparent to particles may be small in diameterto enhance its strength. The emission window may be connected through amedium-to-high electrical resistance path to the enclosure so as tobleed off excess charge from passing charged particles, while notsubstantially diminishing the current of the charged-particle beam.Electrostatic lens elements, which may comprise disc-shaped elementshaving apertures along the beam path, may be used to structurallysupport the emission window. This may substantially avoid introducingadditional structural elements for mechanically supporting the emissionwindow and therefore avoid structural complexity.

Certain optical components, such as components that are very near sample20 during imaging, for example the beam scanners, may be placed afterthe emission window and therefore outside of the enclosure, but maystill be part of the sealed column module. Placing such components afterthe emission window may allow larger deflections than might otherwise bepossible due to the limited diameter of the emission window.Alternatively, such optical components may be placed before the emissionwindow and therefore inside of the enclosure.

In one version, the emission window is energized with an electricpotential to place a charge on axis of the beam. This charge on axis maybe selected to alter aberrations or to correct deleterious aberrationsfrom other parts of the optical system, thereby improving the resolutionperformance of microscope 10.

Alternatively or in addition, the volume separators may be apertures.These apertures may be referred to as differential gas flow apertures.These apertures may be, for example, 0.5 mm aperture inserts, or 1 mmapertures which form electrodes of lenses. Differential gas pressurewould typically cause a jet of gas particles traveling from the volumewith higher pressure toward the volume with lower pressure, and such agas jet can exacerbate beam scattering locally until the beam passessubstantially through the jet. These apertures, however, can limit thegas flow between volumes, due to their small size, and thereby mitigatesuch gas flows to suitable levels.

The charged-particle beam need not necessarily travel through thecenters of the gas flow apertures, or through the apertures at all. Anyof the apertures, for example, may be auxiliary to and placed apart froma separate and smaller aperture that is provided for the beam path.

In the case of a tungsten filament, the overall pressure differencebetween the inner volume of the column module and the externalenvironment may be, for example, from about 10 Torr to about 1×10⁻¹⁰Torr, such as about 1×10⁻² Torr. The inner volume of the column may alsohave substantially different gaseous composition. For example, the innervolume may have a relative absence of water vapor or reactive elementsin relation to the external environment. Alternatively, the inner volumemay have a gaseous or liquid leak that provides replenishing, healing,or restorative elements to the optical elements in the inner volume,such as to the filament area.

A sealed module containing a charged-particle gun system may besealingly enclosed such that a pressure difference between different, oreven identical, species of gases or liquid can be maintained between aninner gun volume and the external environment. In the case of a tungstenfilament, the overall pressure difference may be 10 Torr to 1×10⁻⁵ Torr,with a nominal value of 1×10⁻² Torr. The inner volume may have asubstantially different composition, for example, substantial absence ofwater vapor and reactive elements, in contrast to the externalenvironment.

In order to reach pressures of less than about 1×10⁻² Torr in aparticular volume, a turbo-molecular pump, or molecular drag pump,diffusion pump, or other suitable high-vacuum pump, may be used for thatvolume, in addition to a roughing pump. In order to reach pressures atleast as low as about 1 Torr in a particular volume, meanwhile, only aroughing pump (e.g., diaphragm pump, scroll pump, or rotary vane pump)may be used.

A modular microscope system may comprise several modules that are easilyinterchangeable and replaceable. FIG. 7A is a schematic side view of anexample of an embodiment of such a modular microscope. In this example,the modular microscope include a column module 420, column mount 430,accessory mount 440, microscope base or stage mount 450, accessorymodules 460A, 460B, 460C, and stage 40.

In this embodiment, the optical column may be split into two vacuumvolumes V1 and V2, and the sample chamber encloses a third vacuum volumeV3. Differential pumping enables separation of the vacuum volumes V1-V3,where pressures are related as V1<V2<V3. The V1 volume and V2 volume mayrepresent the same volume and pressure in some versions.

Differential pumping enables smaller pumps to be used with themicroscope, as only one strong pump may be needed for volume V1 and theremaining volumes may be pumped through apertures, or separately byweaker pumps.

The column module 420, accessory modules 460A, 460B, 460C, and stagemount 450 may be quickly and efficiently exchanged for other modules.This for example allows columns of different types to be swapped out—forexample, charged-particle columns of varying types (e.g., high current,large or small working distance, high resolution), or even light-opticalcolumns. Column module 420 may have a feedthrough 470A to providecommunication across the vacuum barrier.

Accessory mount 440 separates column mount 430 from stage 40. Withinaccessory mount 440, an array of connection points 480 surrounding thecolumn perimeter allows attachment of varying accessory devices. Thesedevices may provide mechanical, electrical, and physical (i.e., gaseous)inputs/outputs. These inputs and outputs may be standardized, and arecollected together and efficiently connected to the outside world via asingle or small number of feedthroughs 470C. FIG. 7B is a schematicdiagram of a top view of an accessory mount 440 having feedthrough 470B.

The coupling between column module 420 and column mount 430 may beimplemented as a bayonet or other quick-release mechanism, permittingthe mechanical, electrical, and gas connections to be made substantiallysimultaneously in a single quick movement. FIG. 7C is a schematicdiagram of a side view of an example of one embodiment of column module420 inserted into column mount 430. This enables fast exchange of columnmodule 420 from column mount 430.

FIG. 8A is a schematic top view of a multi-accessory printed circuitboard (PCB) 490 that has eight (8) standardized connection points (alsoreferred to as “accessory bays”). For example, the regular-typeconnector (bays 0-6) 500A may include a high-density quick-release lowand medium voltage connector, whereas the high-current/high-voltage typeconnector (bay 7) 500B may include a lower density array of connectorsthat are able to support higher currents or voltages than the highdensity ones. In this figure, two of the connectors (bays 0 and 4) areshown as populated with accessory modules 460D, 460E while the otherbays are empty.

FIG. 8B is a cross-sectional side view of Section A-A in FIG. 8A. Thisfigure shows PCB 490 is mounted on a frame of accessory mount 440. Ascrew 510 holds accessory module 460D in the bay and electricalconnector 520 to connect accessory module 460D to PCB 490. FIG. 8C is aschematic top view of one of the regular-type connectors 500A shown inFIG. 8A, showing electrical connector 520 and screw hole 530.

FIG. 9A is a schematic perspective view of PCB 490 shown in FIG. 8A. PCB490 may be connected to feedthrough 470B through a wiring harness 540.FIG. 9B is a three-dimensional rendered perspective view of PCB 490shown in FIG. 9A.

Such a modular microscope may provide several advantages. First, themodular microscope clearly defines interfaces between subsystems suchthat core component and accessory structure interconnections arestandardized. Second, the sample volume is well-defined and does notsubstantially interact with optical system or accessories. Third,electrical interfaces and feedthroughs may be simple, optimized, andconstrained, while affording ample expansion opportunities and variationof installed subsystems.

Additional optical components, such as lenses, stigmators, deflectors,beam splitters, and prisms may be implemented as respective modules toaugment the functioning of the system. Such elements may allow forcapabilities such as beam blanking, interferometry, holography, andother types of unique measurements by affecting the beam shape orgeometry just above the sample.

Microscope 10 may additionally contain a compact evaporator to preparethe sample by evaporating metal or another contrast-enhancing agent suchthat the evaporant deposits onto the surface of the sample. The compactevaporator can be a component of microscope 10, and, when placedtogether with sample 20 inside the chamber of microscope 10, canevaporate the contrast-enhancing agent onto the sample in situ.

FIG. 10A is a schematic side view of an example of an embodiment of acompact evaporator 550. Evaporator 550 may have a heated filament 560and a reservoir of evaporant wire 570. Evaporant wire 570 may be inspool or rod form, for example. A motor system 580 may advance evaporantwire 570 onto heated filament 560, whereupon heated filament 560 meltswire 570 and wicks it into filament 560, from which the wire material isevaporated (as evaporant 590 shown in the figure). Evaporator 550 mayalso have a shield 600 to prevent over-spray of evaporant 590 and todirect evaporant 590 onto the sample. Shield 600 may have an aperturecowl over filament 560 to achieve this. Further, evaporator shield 600may protect the detectors from the spray of evaporant, which couldotherwise become coated with evaporated material; this can enable livedetection of sample 20 and monitoring of the evaporation and depositionprocess. A human user may thus be able to monitor and throttleevaporator 550 so as to select the amount of evaporant 590 that is tocoat sample 20.

Evaporator 550 may be compact and enclosed in a small form factor,making it suitable for installation inside sample chamber 100 ofmicroscope 10. For example, evaporator 550 may have a form factor offrom about 1×1×1 cm to about 3×3×3 cm in size, such as about 2×2×2 cm insize in one example. FIG. 10B is a schematic side view of an embodimentin which evaporator 550 is located inside the chamber of a microscope,at a location that is vertically between column 340 and sample 20. Thisfigure also shows that evaporator 440 may have electrical terminals 610to receive power from a power supply.

Microscope 10 may also have a protective screen module to shield thecolumn from a process, such as a reactive etch, sputtering, orevaporative deposition, that the user may want to shield the sensitivecolumn from. FIG. 11A is a schematic side view of an example of anembodiment of a protective screen module 620 in microscope 10 to protectfrom a process 625. A screen 630 may be attached to, and extend from, amechanical mount 640 by an arm 650. For example, screen 630 may be asolid sheet that can be introduced and retracted mechanically.Alternatively, screen 630 may be an adjustable aperture mechanism, whichmay be opened by rotating a ring. FIG. 11B is a schematic top view of anexample of this type of assembly, where the “X” marks a possiblelocation for the beam to pass through the opened aperture assembly. Whena motor 660 is actuated, rotating the exterior ring, aperture 670 closesthereby shielding the column from the process.

Furthermore, a scanning light microscope (SLM) module may be providedinside microscope 10, SLM module being communicatively coupled tocontroller 10 to provide a hybrid scanning light and charged-particlebeam microscope that has novel and synergistic features.

The SLM may include a laser module with optics to produce a smallfocused spot on a sample. A scanning module that contains scanningelements, such as mirrors that tilt in multiple axes, positions the beamspot on sample 20. The beam is scanned in a pattern on sample 20, and adetector detects the signal produced by the interaction of the beam withthe sample. This signal may include reflected light or a fluorescentsignal.

In a combination scanning light and charged-particle microscope, bothtypes of scanning microscopes are included in a single system. For bothscanning microscope types, the distance of the focused spot from thefinal optical focusing element is referred to as the “working distance.”The system may be light-insulated from the external environment so as toavoid detection of stray light from the environment. It may also, butnot necessarily, be enclosed in a vacuum to prevent scattering ofcharged particles by gas molecules or ions. The SLM module may alsodetect reflected color by using filtered detectors or different coloredlaser beams.

Advantages include that one scanning system and one detector system canbe shared between both optical systems. Furthermore, the hybridmicroscope can provide disparate fields of view: (1) a scanned lightfield of view, which may be a larger field of view that allows ahigh-speed survey at lower magnification and lower resolution, and (2) ascanned charged-particle field of view, which may be a smaller field ofview that allows higher magnification and higher resolution. The hybridmicroscope may also permit colocalization of light-optical andcharged-particle signals, from the same sample, optionally at the sametime. For example color information at low resolution from the scanninglight microscope could be combined with high resolution contrast(grayscale) or energy-resolving information from the charged-particlemicroscope.

Further, sample 20 may be tagged (or “labeled”) with compounds (alsoreferred to as “tags” or “markers”) that have affinity to certain typesof structures, and upon excitation by a laser or electron beam the tagcompound may fluoresce. As one example, a compound tag may be attachedto a protein receptor on the surface of a cell. This fluorescence signalcan enable identification and pinpointing of spatially fine structuresby multiple scanned imaging modalities operating optimally at differentlength regimes. Sample 20 may be probed by both light andcharged-particle optical systems in succession, or in parallel, so as totake advantage of the variety of signals that microscope 10 makesavailable in this combination.

In one version, microscope 10 is a scanning charged-particle beammicroscope, such as, for example, a STEM or SEM. FIG. 12A is a schematicside view of an example of an embodiment of a hybrid SLM-SEM 680A. Inthis example, a scanning light microscope module 690 has a laser module700 that is placed perpendicular to charged-particle column 340 ofmicroscope 10. This allows it to be placed outside of the inner vacuumspace of microscope 10, and coupled to vacuum space by a transparentwindow 710. Module 690 also includes optical elements 720 to direct andscan the laser beam onto sample 20.

In an alternative embodiment, shown in FIG. 12B, laser module 700 isplaced parallel to charged-particle column 340, either to the side of(and within the vacuum space) or above column 340 (and outside thevacuum space). This enables a more compact arrangement and places theoptics of scanning light microscope module 690 away from the region ofsample 20, freeing up room for detectors and sample-treatment devices orother devices. Again, module 700 also includes optical elements 720 todirect and scan the laser beam onto sample 20. In FIG. 12B, hybridSLM-SEM 680B also contains a compact evaporator 550.

FIG. 12C is a schematic side view of an example of an embodiment oflaser module 700. In this example, laser module 700 has a laser source730 and a lens 740 that generate a focused laser beam 750.

FIG. 12D is a schematic side view of an example of an embodiment ofrespective fields of view of SLM 690 and charged-particle beam portionof microscope 10, respectively, on sample 20. SLM 690 has larger fieldof view 760, while the charged-particle beam portion of microscope 10has smaller field of view 770. This illustrates the potentialadvantageousness of the larger field of view 760 of SLM 690.

FIG. 13A is a schematic diagram of a light beam passing through asample. ‘D’ is an aperture radius, ‘W’ is the distance from theaperture, and ‘t’ is the numerical aperture. For small ratios of D/W,t≈D/W. In light optics, the diffraction limit diameter ‘d’=1.22λ W/D.Then the depth of field DOF=d/t.

FIG. 13B is a schematic diagram of a light beam being scanned across asample. The field of view ‘FOV’ is limited by the scanning angle. Forexample, certain examples of corresponding focal lengths, beam sizes,depths of focus, and maximum fields of view are provided in Table 1below.

TABLE 1 Focal length 10 20 50 100 200 (mm) Beam size 5.2 10.4 25.9 51.8103.6 (μm) Depth of 104 415 2,591 10,364 41,457 focus (μm) Maximum 2,0395,774 22,911 65,216 186,773 field of view (μm)

Charged-particle microscopes may have a charged-particle detectiondesign in which charged particles emitted from the sample or some othersource are detected by being converted to photons by a scintillator andthen detected by a photon-sensitive detector (e.g., photomultiplier, pindiode, or CCD).

In general, electron microscopes use detectors that are only capable ofdirectly measuring the intensity (or phase) of the electrons, and nottheir energy. This produces only a single value per pixel, i.e., agrayscale image (if energy of the electron was measured too, that couldbe used along with intensity to produce a color image). These grayscaleimages may be processed after acquisition to add color to certain areas(and not others) to enhance the visual appearance of the image. Anexception is in backscatter detection, in which some energy filteringmay occur in the detected signal by geometry, due to the relationshipbetween scattering angle and composition in sample 20.

Alternatively, however, these same detectors may be used to detectphotons directly. These photons could be reflected from the sample as aresult of illumination by, e.g., a laser source. Thus, color images canbe produced in a number of ways. One way would be to place coloredfilters in front of the detector and then combine signals from differentcolored filters to find the emitted color. Another embodiment may entailchanging the color of the laser beam and not use filters in front of thedetectors. A combination of both methods may also be used.

The detector may also be adapted to be tuned to be sensitive to aspecific color or range of colors if such information is desirable. Oneuseful application of this may be to provide color information to agrayscale charged-particle detected image. Generally the resolving powerof focused light is lower than that of charged-particles, but this maybe less of a problem for the color information than for intensityinformation. Combining color information from a photon sourced scannedimage with a charged-particle image could provide high resolution (fromthe charged-particle image) combined with accurate color information.

It can therefore be possible to either collect both signalssimultaneously or, alternatively, one after the other. The processing toproduce a live image could be done in real-time or, alternatively,off-line.

Microscope 10 may include or be connected to a power supply thatprovides power to components of microscope 10. The power supply mayinclude one or more individual power supplies, such as set to differentvoltages or otherwise taking different forms.

In a charged-particle beam microscope, the components that receive powerfrom the power supply may include a charged-particle beam source (e.g.,electron beam source 35), condenser lenses (e.g., condenser lenses 170A,170B, 170C), the objective lens (e.g., objective lens 180), thedetectors (e.g., detectors 210A-E), and the stage (e.g., stage 40). Thepower supply also provides power to the pumps of microscope 10, and toany other components of microscope 10 that consume power. In oneembodiment of a charged-particle beam microscope, the optical system ofmicroscope 10 has a total power consumption for all such components ofless than about 2.5 kW. In another embodiment, designed for powerefficiency, microscope 10 is a charged-particle beam microscope that hasa total power consumption of less than about 1 kW. In yet anotherembodiment optimized for very high efficiency, microscope 10 is acharged-particle beam microscope that has a total power consumption ofless than about 100 W.

In a charged-particle beam microscope, the power supply can provide oneor more voltages to accelerate the charged-particle beam. In oneversion, the power supply includes at least one high-voltage supply,which may be used for a number of lenses. A single high-voltage supplythat may be used to provide the primary beam energy can be modified withresistors to provide multiple values to different lenses that are at aratio of the primary high-voltage value of the high-voltage supply.These resistors may be either constant or programmable by thecontroller. In this manner, instabilities that may be present in thehigh voltage signal can be provided substantially equally to themultiple lenses and the effects of the instabilities can be lessened.The power supply may also include one or more low-voltage supplies, suchas to provide lower voltages to non-round lenses, such as dipoles,quadrupoles, and octupoles.

An embodiment of microscope 10 that incorporates electrostatic lenses,fixed-magnet lenses, or hybrids thereof, in optical components, may beable to consume more than an order of magnitude less power than aconventional charged-particle microscope. Such a very-high-efficiencymicroscope may be capable of a total power consumption of less thanabout 100 W. An example of a very-high-efficiency electron microscope isthe “Mochii” microscope available from Mochii, Inc., of Seattle, Wash.

Microscope 10 may have a battery power supply to provide power from oneor more batteries that has intrinsically low noise (e.g.,electrochemical cells natively have very low noise floor). This mayprovide certain advantages, especially for charged-particle beammicroscope. For example, the battery power supply may reduce thephysical size of the supply if the runtime requirement and additionalweight from the battery bank are balanced. The battery power supply maybe used to power subsystems, such as for example the filament of thecharged-particle beam source, an accelerator, or lenses, or the entiremicroscope. The battery may include electrochemical cells (e.g.,lithium-ion battery), electrochemical capacitors such as asupercapacitor, a fuel cell, one or more other suitable energy-storagemodules, or any suitable combination of these. In one example, thebattery power supply powers one or more subsystems or an entiremicroscope consuming less than about 275 W. In another example, a“Mochii” microscope that consumes less than about 200 W when fullyenergized, including all components (such as optical system, powersupplies, pumping systems, controllers), is commercially available fromMochii, Inc. (d/b/a Voxa) of Seattle, Wash.

In one version, microscope 10 has a solar-power supply to generateelectricity from ambient light. The solar-power supply may include, forexample, one or more photovoltaic cells that are configured to receiveambient light. The photovoltaic cells may optionally be arranged in anarray. In one embodiment, the solar-power supply works together with thebattery power supply, such as including charging the battery powersupply. The solar-power version may be especially suitable for amicroscope that is optimized for very high power efficiency.

Since filament supplies in many applications, such as electronmicroscopy, are run at high negative voltage relative to the powersource, which is typically at ground potential, a battery power supplycan provide an efficient way to transfer power in a single transitionevent. Additionally, the battery power supply may enable the filament tobe energized without the presence of AC in the filament supply line,eliminating frequency noise from the filament and improving performancein critical applications using minimal componentry.

Since conventional filament supplies of charged-particle beammicroscopes are often run at large potentials relative to ground, thetransformers that provide the power to these supplies must typicallyhold high voltages. The power to be transferred is often considerable(on the order of 5 W), and in many sensitive applications the ACoutputted from the transformer must be converted to a very stable DC forthe filament. As a result the transformers are typically large and bulkydue to the need for large spark gaps, exotic potting materials, andlarge conductors. On the output end of the transformer, a precisionregulated power supply—often of the inefficient linear type—is used toconvert the outputted AC to DC for driving the filament. Thetransformers and AC to DC power supplies have native losses as power istransferred, which generates additional heat and less efficiency.

A solution to the drawbacks of conventional filament supplies ofcharged-particle beam microscopes is to use compact battery technologiesto reduce the weight and size of such a supply by eliminating the needfor a large spark gap power transformer and precision DC power supplyregulation. The reduced parts count and bulk enable miniaturization andeasier isolation. Power loss is reduced by eliminating the high voltagetransformer and high precision and low noise DC producing circuitry thatthe filament requires, and using more efficient power supplies such asswitching type to charge the battery. Charging of the battery can beperformed by a charging supply that may not be stable enough orotherwise good enough to directly power a stably running filament in aconventional power supply of a charged-particle beam microscope. Thiscan reduce cost, size, and weight.

In one version, the battery power supply is a multiple-battery bankpower supply, such as a two-battery bank power supply. In this version,battery packs are used in tandem to allow one battery to be chargedwhile the other is active in the system. Thus, continuous filamentuptime can be achieved.

FIG. 14A is an electrical schematic diagram of an example of a firstembodiment of a two-battery bank power supply 780. In this embodiment,two tandem batteries B1, B2 are used to provide DC power to thefilament. Power supply 780 may have continuous runtime set by thecapacity of batteries B1, B2 without requiring a charging supply 790 tobe energized, and indefinite run time with charging supply 790energized. Furthermore, batteries B1, B2 can be kept at high voltage.The DC from active battery B1 (connected to the filament) may beadjusted with a small regulator while inactive battery B2 (connected tothe charging supply) is being charged. A transformer may supply a chargecurrent to charging supply 790, which continuously charges inactivebattery B2. When active battery B1 is depleted, freshly charged batteryB2 is switched in to power the filament and the depleted battery is putinto the charging mode.

FIG. 14B is an electrical schematic diagram of an example of a secondembodiment of two-battery bank power supply 780. This embodimenteliminates the 10 kV transformer as well as the AC-DC and replaces itwith a charging supply 790 kept at low voltage. Batteries B1, B2 areable to be placed at either high voltage or at low voltage by aswitching system 800 capable of maintaining the high voltage difference.Similar to the first embodiment, power supply 780 has continuous runtimeset by the capacity of two batteries B1, B2 without charging supply 790energized, and indefinite run time with charging supply 790 energized.

Microscope 10, which may be a charged-particle beam microscope or alight microscope, may include a controller to control various aspects ofoperation of microscope 10. The controller may, for example, receiveinputs from a human user, provide instructions or other signals tocomponents of microscope 10, and/or perform data processing of signalsdetected by microscope 10 to generate and process images. For example,the controller may control the components of the optical column ofmicroscope 10, such as, in the case of a charged-particle beammicroscope, the charged-particle beam source, beam scanners (e.g., beamscanners 170), and the detectors, as well as the stage. The controllermay also receive signals from the detectors (such as detectors 190A-E)to be processed computationally to generate images. The controller mayinclude an image formation unit for this purpose. The image formationunit may be disposed within or external to the microscope column andcommunicate with the optical system and the stage in any fashion, suchas by a direct or indirect electronic coupling, or via a network. Thecontroller may automatically handle one or more aspects of operation ofmicroscope 10, and may even be adapted to substantially automate theoperation of microscope 10 with minimal input required from a humanuser.

The controller may include one or more microprocessors, controllers,processing systems, and/or circuitry, such as any combination ofhardware and/or software modules. For example, the controller may beimplemented in any quantity of personal computers, such asIBM-compatible, Apple, Macintosh, Android, or other computer platforms.The controller may also include any commercially available operatingsystem software, such as Windows, OS/2, Unix, or Linux, and anycommercially available and/or custom software such as communicationssoftware or microscope monitoring software. Furthermore, the controllermay include one or more types of input devices, such as for example atouchpad, keyboard, mouse, microphone, or voice recognition.

The controller software may be stored on a computer-readable medium,such as a magnetic, optical, magneto-optic, or flash medium, floppydiskettes, CD-ROM, DVD, or other memory devices, for use on stand-alonesystems or systems connected by a network or other communicationsmedium, and/or may be downloaded, such as in the form of carrier waves,or packets, to systems via a network or other communications medium.

Microscope 10, which may be a charged-particle beam microscope or lightmicroscope, can be controlled using at least one terminal having a userinterface (UI) that communicates with microscope 10, such as via thecontroller. Either all or a subset of the functionality of eachcomponent may be exposed to the UI. The UI may automatically makechanges to the components based on information it receives from theuser, from other components, and/or at certain times or locations. TheUI may thereby offer a simplified way to control various components ofmicroscope 10.

Microscope 10 may be operated by a portable device providing that UI inthe form of hardware and/or software. The portable device may be, forexample, a tablet computer, smartphone, or other consumer device. Forexample, this UI may be a secondary interface, where a terminal that islocal to microscope 10 constitutes the primary interface. This secondaryinterface can provide some or all of the functionality of the primaryuser interface, such as complete operation of microscope 10. Any numberof these secondary interfaces may be adapted to control the instrument.

The UI may include a touch-screen interface to enhance interaction ofthe user with the microscope. For example, a pinching movement of thefingers or hand on the touch-screen may cause the image to grow orshrink. Dragging with a finger could cause the stage to move. It mayalso shift the current image immediately, estimating the appearance ofthe next image to acquire. Other gestures could perform other operations(e.g., two-finger drag could change astigmatism, etc.) The user coulduse a touch screen interface to perform all necessary actions on themicroscope. These could include moving the sample, changing the field ofview, focusing, stigmating, or otherwise tuning the image, changing thesample dwell time, changing the resolution, changing source intensity,etc. The UI may also be configured to synchronize and mediate betweenmultiple devices connected to microscope 10.

The controller and the UI may provide two-way communication between thehuman user and microscope 10, such as feedback-based control ofmicroscope 10 by the user. For example, the user may make a gesture atthe UI, such as a swipe of a finger, that causes a stage movement orbeam displacement to shift imaging in proportion to the swipe. The UImay then quickly refresh the image provided to the user for the newimaging location. The user may also make a gesture at the UI to change,for example, one or more imaging perspectives, brightness, or contrast,which may control detectors of the microscope, such as by turning themon or off or by triggering actuators that change the detectors'positions. For feedback-based control of microscope 10, it may bedesirable to have two-way communications between UI and microscope 10with suitably low latency in relation to human visual and tactilesenses, and at least one-way communication from microscope 10 to UI withsufficiently high throughput to provide images to the user sufficientlyquickly to give the user a sense of “real time” performance. In oneembodiment, lower-resolution survey images may be provided to the userin substantially real time, and at a selected imaging location the usermay request a higher resolution image that is not provided in real time.In one example, microscope 10 and the UI are adapted to have the stagerespond to user commands with a latency of less than about 100 ms. Inanother example, microscope 10 and the UI are adapted to respond to usercommands and give feedback or send a complete image from microscope 10to the UI in less than about 1,000 ms, and preferably less than 500 ms.

The UI may be adapted to attempt to perform as many operationsautomatically as possible. For example, starting an application, orturning the device on may be interpreted as the user wanting to operatethe microscope and it can attempt to turn on the microscopeautomatically. This could also happen in response to actions taken onthe instrument itself; e.g., closing a door could interpreted as a cueto turn on the microscope. The microscope may be kept as “on” aspossible, depending on power requirements or longevity of components.

As one example, automation may be provided around the changing of asample in a charged-particle beam microscope (EM). Changing the samplemay require venting to air a previously evacuated area, and may involveramping the source voltage down to a safe level. Both steps may beperformed automatically when the user starts the sample change. Once thechange is complete the area is automatically evacuated and the highvoltage automatically turns on. (If the instrument is running onbatteries, however, this step may be postponed until later to preservebattery power.) The microscope would automatically get itself as readyas possible for imaging, for example ramping the filament to atemperature at which its lifetime is not shortened, but it remains nearenough to the operating temperature that normal operation can beachieved relatively quickly without any stress to the filament. At thispoint the user could start the tablet computer, smartphone, or otherconsumer device, or even visit a website, at which point the microscopeis automatically turned on fully (if running under batteries, this couldbe the point at which it performs the previous steps mentioned, havingpostponed preparation of the microscope for imaging until needed topreserve battery life).

Once the user has indicated that the imaging session is over, whichcould be either via a preprogrammed time limit, period of inaction or byclosing an application, leaving a website, putting a device to sleep, ora suitable alternative method, the microscope returns to a “ready” statewhere the filament longevity is not reduced but the microscope is readyto start at a moment's notice. An example of the “ready” state mayinclude leaving the high voltage energized and stable while turning thefilament to a reduced current level to protect its longevity. If runningunder battery power, the microscope may skip this state and return toits minimum power state as soon as possible.

At some other point the microscope could enter its power off state, iffor example an off button was pushed or an option in the softwareselected or some other indication that the microscope needed to powerdown. This could even be having the mains power removed from themicroscope. At this point the microscope would safely shutdown anyremaining components.

Power supplies and accessories of microscope 10 that operate at highpotentials relative to ground may require communication over anisolation barrier to set voltages, measure values, and perform othertypes of control and/or acquisition operations. This may be accomplishedusing opto-isolators.

However, in another version, electrically isolated communications for anembodiment of a charged-particle beam microscope can be achieved using awireless computer system. The receiver at the high voltage side (i.e.,the microscope) may comprise a low-power microcontroller and powersupply. The power supply may be derived over a potential gap using atransformer, or the microcontroller may be capable of being run off ofbattery power for an extended duration due to its low-power operation.Additionally, the power supply may be charged through inductive meanswhile not operating.

FIG. 15 is a schematic diagram of an example of an embodiment of asystem for electrically-isolated wireless communications between a userinterface (UI) 810 and a charged-particle beam microscope. In thisfigure, the items enclosed in the dashed line are at high electricalpotential, whereas items outside of the dashed line are at lowelectrical potential or ground potential. UI 810 may be implemented on acomputer. The computer communicates with a controller 820 of microscope,which can control the microscope and/or read back data or other signalsfrom the microscope. For example, controller 820 may control and/or readback data from power supply 830 for the charged-particle beam sourcefilament by transmitting and receiving control commands and data throughthe wireless path, as shown.

One or more of the features of a charged-particle beam microscopedescribed above—such as, for example, a monolithic optical column,modular subsystems, low power consumption, and the use of a remoteand/or wireless UI rather than a local terminal—may allow microscope 10to have an advantageously low weight. For example, microscope 10,including its controller and pumping system, may be adapted to have aweight of less than about 50 kg, or even less than about 30 kg. Forexample, a “Mochii” microscope weighing less than about 20 kg, includingall components (such as optical system, power supplies, pumping systems,controllers, and UI devices), is commercially available from Mochii,Inc. (d/b/a Voxa) of Seattle, Wash.

Microscope 10 may have a characteristic area at the plane of sample 20in which certain imaging characteristics, such as, for example,resolution or other optical characteristics, are selected to be within arange suited to the imaging that is performed. This area may be referredto as the “field of view” of microscope 10 for certain versions. Withinthe field of view, a charged-particle beam or light beam may be scannedin one or more scanning areas across sample 20 while remaining withinthe desired range of optical characteristics (such as high resolution).In the case of a charged-particle beam, the scanning may be performed byelectronic shifting, such as by generating an electric or magneticfield,

Within each field of view, microscope 10 may define one or more scanningareas of sample 20 (e.g., areas in which a charged-particle beam orlight beam will be scanned) contribute to the final image. Microscope 10may perform the imaging of sample 20 in one or more cycles correspondingto the scanning areas, each imaging cycle for a scanning area yielding acontribution that is referred to here as a sub-image. Each scanning areamay be noncontiguous, contiguous, or overlapping in relation to scanningareas within the same field of view or scanning areas in differentfields of view. Moreover, the scanning areas may even be a combinationof noncontiguous (i.e., with edges separated by a space), contiguous(i.e., edge to edge), or overlapping.

The controller may stitch together the sub-images to produce a partiallyor wholly comprehensive image of sample 20. For example, where there areoverlapping or contiguous sub-images, these sub-images may be joinedtogether to yield imaging data that is continuous across thecorresponding scanning areas. For overlapping sub-images, the controllermay use the redundant image information at the overlap to accuratelyjoin the sub-images together into a comprehensive image. The controllermay automatically control the acquisition of sub-images along a setpath, for example a raster pattern or a zig-zag pattern. Further, newdata may automatically be integrated into a large map (e.g., a map ofsubstantially the whole sample) as sub-images are acquired so as to fillin the large map with available information.

In a scanning microscope (e.g., a confocal light microscope, STEM, SEM,atomic force microscope, scanning tunneling microscope), the precisescan paths may even be defined according to the particular application.For example, the location of the beam or probe can be set to anyposition, for any time duration, along the scan path.

In one version, as a new image is being acquired, the controller alignsor otherwise conforms the new image to one or more previously generatedimages. For example, the controller may process newly detected pixeldata to decide on or alter future imaging locations, such as to fill ingaps in imaging or to try to align the new image vertically orhorizontally with one or more of the previously generated images. Inanother example, the controller processes newly detected pixel data todecide on or alter future image resolution or time spent at a particularlocation. For example, the controller may estimate a likely significanceof the image at a predetermined location, and the controller may usethat estimate to increase or decrease resolution or another imagequality parameter for imaging at that location or nearby. Theseadjustments can alternatively or additionally be calculated betweenimaging cycles to affect the next new cycle of image acquisition.

In one embodiment of a scanning microscope, the controller controls thestage and/or beam scanners to move the beam or probe relative to thesample in a stochastic, path-dependent, or self-correcting fashion. Thismay be especially advantageous for electron beam microscopy due to therelatively fast response time of the electron beam to the scanningsignal. For example, the controller may start creating an image byshifting the electron beam a small amount using a selected one of thebeam scanners. The controller may then measure the magnitude of theshift actually produced, and use that measurement to change the amountand direction of the next shift. After more shifts and measurements havebeen performed, the controller may learn the strength, direction, andrepeatability of the beam scanners and/or the stage. The controller maythen use this learned information to produce substantially orthogonal orotherwise intentionally directed shifts at a suitable distance forstitching a larger image together. Furthermore, the controller may usethe early images, although not acquired using optimal shifts, to preparethe stitched images, such that the time spent characterizing the shiftsis not wasted.

Although performing these steps while images are acquired live ispossible, the analysis may also be performed off-line. Although it maynot be possible to optimize shifts for the previously acquired imageafter it has occurred, that image may provide useful information forfuture image acquisitions.

As another example, as an image is tiled, areas of low or zero contrastmay be identified. When images from that region are next imaged, theimaging system could spend less time on that area, or measure it at alower resolution. This could be done at a faster rate than whenacquiring normal quality images and lead to a speed up in total imageacquisition time, while not affecting the quality of the image in theimportant areas. Lower quality images can be checked to insure that theyreally do represent a low-interest region, and if it is determined theydo not, the image could be reacquired at higher or regular resolution.

The controller may also be adapted to increase the quality of the imageat or near a feature of interest, and decrease the quality of the image(while increasing imaging speed) with increasing distance from thatfeature of interest.

The controller of a scanning microscope may also control the stageand/or beam scanners to produce alternative scanning patterns. Forexample, the controller may scan the beam or probe across the sample inspace-filling curve patterns. Space-filling curves may include, forexample, a Hilbert curve, Peano curve, or another suitable type ofprogressively finer scanning curve. These scans can achieveprogressively finer detail over time, such as by incrementallyincreasing the order of the curve, allowing users to decide whether tocontinue scan based on coarser, earlier data.

The above methods could be applied in real-time to data as it isacquired and shown to the user immediately. The user could then cancelthe acquisition if needed or manually highlight areas of interest thatcould be acquired at higher quality.

In one version, microscope 10 may generate at least two types of imagesof sample 20. The first category is survey images, which may be taken togenerate a high-framerate survey video. These survey images may be usedfor tuning the microscope, and finding the appropriate area of thesample on which to conduct more detailed imaging. The second category ishigh-resolution images. When imaging in the high-resolution mode, themicroscope may be slower and less responsive than in the survey mode,but can provide more detail and less noise than the survey images, orsignals that may be unavailable at high framerates (e.g., x-raycomposition data).

In one embodiment, microscope 10 performs a preliminary,lower-resolution imaging of sample 20 before a principal,higher-resolution imaging of sample 20. The preliminary imaging may be,for example, a faster or lower-dose scan of sample 20 used to determinethe locations of one or more features of interest in sample 20. Thesefeatures may include, for example, a specific cell body with a tag thatsets it apart from other cell bodies, or each of multiple polymerstrands. This scan may, in one embodiment, cover a substantiallycontiguous area, rather than being limited to particular and discretescanning areas. Surveying may also be performed outside of microscope10, where fiducials on sample 20 or another registration mechanism isprovided, such as using a different type of charged-particle microscopeor alternatively an optical microscope (such as for fluorescent orlight-visible tags).

The controller may then define the scanning areas such that the scanningareas track sample 20 based on the determined location of sample 20. Bydefining scanning areas that track sample 20, microscope 10 may be ableto avoid even more empty area where areas of interest of the sample arenot present, eliminating wasteful acquisition of pixels and providingeffectively faster imaging speeds. Using the scanning areas, thecontroller may perform a slower or higher-resolution scan within thescanning areas, thus concentrating the imaging on the actual location ofsample 20 and thereby improving efficiency. For example, within eachscanning area microscope 10 may raster scan the beam or probe.

Data streamed from microscope 10 by the UI may be adjusted dynamicallyand automatically such that the user experience is enhanced based on theUI context. For example, microscope 10 may be configured toautomatically transition between data densities and latencies based oninput from the user to provide an improved user experience. Further,microscope 10 may be configured to predictively acquire and cache imagedata to be served on a contextual basis to the client UI. Whileadjustment of datastream mode and latency can be applied toserially-acquired data as well, the above description also applies dataacquired through parallel means, such as from a CCD camera.

It is typically desirable to have the image that is produced by theimaging system accurately represent information in the sample needed foranalysis. In the ideal case of perfect imaging, the image faithfullyreproduces the features of the sample that are needed for analysis. Inthe real world, however, imaging is often imperfect. In some cases,distortions due to imperfect imaging conditions can result in a warpedimage. In beam-optical microscopes, these distortions may be caused, forexample, by instabilities in the environment such as stray electric ormagnetic fields, mechanical vibrations, temperature fluctuations, orinternal instabilities such as power supply ripple, ground noise, orperiodic electrical discharges.

In a beam-optical microscope, the controller may be adapted toautomatically diagnose the magnitudes of various aberrations and applycompensating signals to the optical system, such as to one or more ofthe optical elements that may cause aberrations and/or the aberrationcorrector (e.g., aberration corrector 90). Microscope 10 may beespecially adapted to correct for two types of image distortions: (1)distortions that are periodic in time, and (2) distortions that arestatic in time. An example of the first type involves displacement ofthe beam-probe location due to mains AC fields.

One exemplary method is to raster scan one or more tuning regions ofsample 20 to generate an image and to analyze the generated image toextract information about aberrations that can be used to correct theaberrations. The tuning regions may be of any shape or size and may belocated within or outside of the areas to be scanned.

Distortions can be diagnosed by analyzing images of the same sampletaken using different scan parameters. Based on the types of distortionsto correct, more images may be generated that have different rotations,sampling frequency, sampling spacing, magnification, etc. Periodic andstatic distortions can be extracted from some or all of the abovecomparisons, based on assumptions about the distortions.

For example, in a conventionally rastered image, wherein the fast “x”direction represents the pixel scan that increments each pixel clock,and the slower “y” direction represents the line scan that incrementsonly after a full pixel width of the field of view is acquired, an imagecan be recorded with the fast, “x” direction, then another image of thesame sample can be acquired in a direction that is rotated byapproximately 90 degrees in relation to the previous “x” direction. Bycomparing the location of features between the two images of the samesample, a map of distortion can be calculated across either image.

Another exemplary method for a charged-particle beam microscope is toacquire one or more images as a function of illumination tilt anddefocus, and to extract the blurring effect of the tilt and defocus. Theblurring gives a value for the defocus and astigmatism at a variety ofangles. This process can provide sufficient data to numerically computean aberration function for the imaging system. Yet another method is todefocus the charged-particle beam and use a bright-field detector (e.g.,bright-field detector 210C), such as a CCD camera, to generate aRonchigram image, or a plurality of Ronchigram images taken at differentpositions of sample 20, and then refocus the charged-particle beam forcontinued imaging of the sample. The Ronchigram image can providesufficient aberration information to derive optical parameters thatpermit suitable compensation for these aberrations.

Once distortions are measured the data can be presented to the user as ameasure to help diagnose instabilities. It could also be used as inputto a post processing algorithm to remove distortions. This algorithmcould be applied to future images assuming the distortions remainconstant. It could also be used and fed back in to the scanning unit tocorrect for the distortions by changing the scanning locations (e.g.,moving the beam to a location where adding the measured distortion willplace the beam at the required location). Following the application ofany of these or other correcting techniques, the process could beapplied again iteratively, each time measuring and potentiallycorrecting finer distortions.

A sample used for the purposes of diagnosing aberrations in acharged-particle beam microscope may contain, for example, single atomsor clusters of atoms, or may be another kind of sample adapted to permitmicroscope 10 to diagnose optical aberrations. For example, the samplemay be the same sample 20 that is also the subject of interest forstudy. Alternatively, the sample may be a reference sample used solelyfor calibration of microscope 10. Distortions relative to the knownstructure of the reference sample can then be extracted.

The tuning region may be positioned to account for workflow convenience.For example, the tuning region may be located at a default (or “home”)position of stage 40 so that it may be used to tune microscope 10 priorto imaging sample 20 and the user can always be presented with asubstantially optimized image of sample 20.

In one version, microscope 10 even contains a mechanism for insertingthe reference sample into the beam path for calibration, and retractingthe reference sample when it is not being imaged. In this version, thereference sample may even be kept inside microscope 10 such that themechanism can readily insert the reference sample into the beam path forcalibration of microscope 10.

The reference sample may mounted on a rod, which can temporarily insertthe reference sample into the field of view of microscope 10 forcalibration. The controller may execute this calibration only when thesample to be imaged is first inserted, or alternatively the controllermay execute this calibration repeatedly during operation.

Identification of samples used for conventional microscopy mayconventionally pose a challenge, especially in terms of efficientlyidentifying and imaging multiple samples in sequence. As the number ofsamples to be imaged is increased due to other innovations, keepingtrack of the identities of the samples becomes even more problematic.With the potentially larger number of observed samples due to theseinnovations, keeping track of samples may be even more challenging.Thus, an identification system is described that permits anidentification pattern to be placed on sample 20 and read by themicroscope. This improves the efficiency of identifying and trackingmultiple samples.

An identification pattern may be placed on sample 20 temporarily orpermanently. For example, the identification pattern may be a removablesample label that is placed on sample 20 or a sample holder, orpatterned onto sample 20 or the sample holder using an electron beam ofmicroscope 10 adjusted with elevated current or laser of SLM-SEM 680A,680B. The patterning could be carried out on a beam-sensitive label areaof sample 20, comprising, for example, a beam-sensitive sacrificialpolymer, or an etchable substrate catalyzed by exposure to a beam.Alternatively, the identification pattern may be etched onto sample 20.The identification pattern may contain a unique identification code thatcan be determined when the pattern is read by one or more means. Forexample, the pattern may comprise a miniature bar code, QR code, oranother type of code based on a geometric pattern. The pattern may bevisible to photons and/or charged particles. The identification code maybe inserted into the metadata of images of the sample that are generatedby the microscope, providing convenient tracking of the sample.

A reference pattern may also be placed on the sample to enable quickcalibration of microscope 10, such as focusing in the case of abeam-optical microscope, by imaging of the reference pattern. Forexample, microscope 10 may perform this calibration substantiallyautomatically. The reference pattern may be placed at a location of thesample that is predetermined relative to the stage. The same referencepattern may be used on different samples to enable microscope 10 to becalibrated by imaging the reference pattern.

Furthermore, a combination identification/reference pattern may beprovided in which the pattern provides an identification code and thesame pattern is also used for calibration of the microscope. In thisversion, microscope 10 may, on insertion of the sample, read theidentification code from the pattern and simultaneously calibratemicroscope 10 based on the pattern, readying microscope 10 for imagingof the sample.

As a charged-particle beam microscope is operated, various parametersmay undesirably vary over time. This may conventionally necessitatevigilance and maintenance by the user. For example, the user may have tomonitor the parameters and, for example, instruct the controller to turnoff the charged-particle beam source if a particular value falls below apredefined threshold. This may increase the burden on the user andnegatively impact ease of use of the microscope.

To address this, the controller may automatically monitor importantoperating parameters. The controller may also automatically make changesto keep the parameters within suitable ranges. Alternatively, thecontroller may make these changes at times that are appropriate orconvenient to the user, such as between imaging cycles.

In one example of charged-particle beam microscopy, the controllermonitors the emission current to maintain desired operating conditionsof microscope 10. The controller can change the emission current byvarying the voltage at the Wehnelt. However, doing so while imaging maycause detrimental effects in the images. Therefore, the controller mayvary the voltage at the Wehnelt to make these adjustments at times thatimaging is not occurring.

In another example of charged-particle beam microscopy, the controllermay monitor the filament temperature, resistance, and/or current andadjust the power supply accordingly to keep these values withinpredefined (e.g., user-defined) ranges. The controller may optionallymake these adjustments only at appropriate times, such as when imageacquisition is not occurring.

Thus, by automatically monitoring and correcting those parameters,microscope 10 may substantially avoid the need for human intervention inregard to those parameters and therefore even be able to hide theexistence of those parameters from the user. This can make operation ofmicroscope 10 much simpler and easier for the user, who can in turnfocus on his or her ultimate desired use of microscope 10.

The controller may also evaluate information originating at one or moreof the detectors of a beam-optical microscope, either between imagingcycles or simultaneous with imaging, to determine the current quality ofimaging. In one version, imaging information from dedicated “tuningregions” is used. However, the images themselves may additionally oralternatively be used. For example, information from the most recentimages can be used to determine trends of tuning deterioration. Thisevaluation can be used to set parameters of microscope 10 to improve thequality of imaging. For example, referring to FIG. 1 for the sake ofillustration, the parameters may be applied to condenser lenses (e.g.,condenser lenses 70A-C), the objective lens (e.g., objective lens 100),the aberration corrector (e.g., aberration corrector 90), and the stage(e.g., stage 15). In an illustrative example, the parameters applied tothe condenser lenses, the objective lens, and the stage may improve thefocus, while the parameters applied to the aberration corrector maycompensate for higher orders of aberration. This process may be referredto as “re-tuning” the microscope.

It may be desirable to maintain the microscope in a substantially steadystate in terms of contamination and stability during imaging. But theperformance of the optical system of a charged-particle beam microscopemay tend to deteriorate over time. In one example, the optical system ofa charged-particle beam microscope may deteriorate to an undesirablestate in from about 5 to about 30 minutes, such as about 15 minutes.When this happens, it may become advantageous to perform re-tuning. Inone version, first-order and second-order aberrations may be especiallyprone to deterioration and/or advantageous to compensate for byre-tuning. The charged-particle beam source may also deteriorate overtime. To refresh the charged-particle beam source, it can be “flashed”by running a high current through it between beam scanning cycles. Thiscauses a localized heating of the filament that reconditions the source.

Re-tuning of a charged-particle beam microscope may be triggeredaccording to any suitable procedure. The controller may monitor themicroscope to initiate the determination of imaging quality, thecontroller may automatically initiate re-tuning at regular intervals, orthe controller may poll a store of recently generated images todetermine image quality as a background process. For example, there-tuning may be triggered within any desired time interval, such aswithin any quantity of hours or minutes, or subsequent to any quantityof images generated by the microscope or every Nth linear scan or scancycle performed by the microscope. In an exemplary embodiment, thecontroller initiates re-tuning between sequential fields of view. Inanother embodiment, however, the controller can re-tune the opticalsystem between sequential scanning areas.

At each of the sub-areas, microscope 10 may image a tuning region withinor outside of the sub-area one or more times to generate one or moresub-images that can be used to track the sample and/or produce imagingmetadata. The imaging metadata may include, for example, focus error andamounts of various orders of aberration, and beam current. Thecontroller may use the imaging metadata to modify parameters to improveimage quality, such as, for example, to autofocus the image at theelevation of sub-area. For example, the controller may evaluate severalsub-images taken in a particular area to determine the magnitude anddirection of focus error. Using this information, microscope 10 cangenerate a final well-focused sub-image that will be used for evaluationof the sample itself. Microscope 10 may use any number of sub-images ofa sample to determine imaging metadata. The sub-images may cover anydesired variation range for a particular parameter.

In analyzing an image, the controller may analyze any suitablecharacteristics of the image, such as intensity, pixel counts, or power,each of which may be analyzed in real space or in frequency space (sothat intensity may be within or outside of a spatial frequency range).When comparing images or evaluating a series of images, the controllermay utilize any suitable characteristic that differs between the images,such as in a preselected region of the images.

The controller may also use any number of images for the image qualitycomparison, where the image quality values for current and prior imagesmay be combined in any suitable fashion, such as averaged, weighted, orsummed. A user threshold for image quality may be set to any suitablevalue. A comparison of image quality values may utilize any mathematicalor statistical operations to determine image quality compliance, such asa comparison, statistical variance, or deviation.

The imaging process may be performed automatically, such as afterinitiation by a user or initiation by a larger process of which theimaging is a subprocess. Parameters may be determined automatically andapplied to the microscope. Alternatively, any part of the technique,such as image generation, determination of parameters, or application ofthe parameters, may be performed manually. For example, the controlleror a separate computer system may provide the optimal settings to atechnician who manually applies the settings to the microscope. Themicroscope controller may perform any desired processing, such asmonitoring and adjustment of optical parameters or image formation andprocessing. For example, the controller may align images using imageregistration algorithms. The controller of a beam-optical microscope mayalso adjust the aberrations and defocus of an image based oncharacteristics of a previous image.

Microscope 10 may be used in any suitable facility in any desiredarrangement, such as networked, direct, or indirect communicationarrangements. Moreover, the various functions of microscope 10 may bedistributed in any manner among any quantity of components, such as oneor more hardware and/or software modules or units. The hardware mayinclude microscopes, machine managers, computer or processing systems,circuitry, networks, and image stores, that may be disposed locally orremotely of each other and may communicate with each other or be coupledto each other in any suitable manner, such as wired or wireless, over anetwork such as WAN, LAN, Intranet, Internet, hardwire, or modem,directly or indirectly, locally or remotely from each other, via anycommunications medium, and utilizing any suitable communication protocolor standard. The software and/or algorithms described above may bemodified in any manner that accomplishes the functions described herein.

Microscope 10 described herein, in the case of a charged-particle beammicroscope, may be implemented with either electrostatic or magneticcomponents or a combination thereof. The microscope may include anyquantity of electrostatic or magnetic components, such as an electron orother charged-particle gun, lenses, a dispersion device, stigmators,deflectors, detectors, and stages, arranged within or outside of themicroscope in any suitable fashion.

Image stores, files, and folders used by microscope 10 may be of anyquantity and may be implemented by any storage devices, such as memory,database, or data structures. Implementation of aspects of themicroscope, such as image processing or the user interface, may bedistributed among the controller or other processing devices in anydesired manner, where these devices may be local or remote in relationto one another. The controller may communicate with and/or control themicroscope to perform any desired functions, such as scanning the sampleand generating the images or transferring images to memory.

Although the foregoing embodiments have been described in detail by wayof illustration and example for purposes of clarity of understanding, itwill be readily apparent to those of ordinary skill in the art in lightof the description herein that certain changes and modifications may bemade thereto without departing from the spirit or scope of the appendedclaims. It is also to be understood that the terminology used herein isfor the purpose of describing particular aspects only, and is notintended to be limiting, since the scope of the present invention willbe limited only by the appended claims.

It is noted that, as used herein and in the appended claims, thesingular forms “a”, “an”, and “the” include plural referents unless thecontext clearly dictates otherwise. It is further noted that the claimsmay be drafted to exclude any optional element. As such, this statementis intended to serve as antecedent basis for use of such exclusiveterminology as “solely,” “only,” and the like in connection with therecitation of claim elements, or use of a “negative” limitation. As willbe apparent to those of ordinary skill in the art upon reading thisdisclosure, each of the individual aspects described and illustratedherein has discrete components and features which may be readilyseparated from or combined with the features of any of the other severalaspects without departing from the scope or spirit of the disclosure.Any recited method can be carried out in the order of events recited orin any other order which is logically possible. Accordingly, thepreceding merely provides illustrative examples. It will be appreciatedthat those of ordinary skill in the art will be able to devise variousarrangements which, although not explicitly described or shown herein,embody the principles of the disclosure and are included within itsspirit and scope.

Furthermore, all examples and conditional language recited herein areprincipally intended to aid the reader in understanding the principlesof the invention and the concepts contributed by the inventors tofurthering the art, and are to be construed without limitation to suchspecifically recited examples and conditions. Moreover, all statementsherein reciting principles and aspects of the invention, as well asspecific examples thereof, are intended to encompass both structural andfunctional equivalents thereof. Additionally, it is intended that suchequivalents include both currently known equivalents and equivalentsdeveloped in the future, i.e., any elements developed that perform thesame function, regardless of structure. The scope of the presentinvention, therefore, is not intended to be limited to the exemplaryconfigurations shown and described herein. Rather, the scope and spiritof present invention is embodied by the claims.

In this specification, various preferred embodiments have been describedwith reference to the accompanying drawings. It will be apparent,however, that various other modifications and changes may be madethereto and additional embodiments may be implemented without departingfrom the broader scope of the claims that follow. The specification anddrawings are accordingly to be regarded in an illustrative rather thanrestrictive sense.

We claim:
 1. A charged-particle beam microscope for imaging a sample,the microscope comprising: a stage to hold a sample; a charged-particlebeam column to direct a charged-particle beam onto the sample, thecharged-particle beam column comprising: a charged-particle beam sourceto generate a charged-particle beam, and charged-particle beam optics toconverge the charged-particle beam onto the sample; a light beam columnto direct a light beam onto the sample, the light beam columncomprising: a light beam source to generate a light beam, and light-beamoptics to converge the light beam onto the sample; a detector to detectboth charged-particle and light radiation emanating from the sample togenerate an image; and a controller to analyze the detectedcharged-particle radiation and the detected light radiation to generatean image of the sample.
 2. A charged-particle beam microscope accordingto claim 1, wherein the light beam source is adapted to generate a lightbeam having one or more preselected wavelengths.
 3. A charged-particlebeam microscope according to claim 1, wherein the controller is adaptedto operate the charged-particle beam column, the light beam column, andthe detector to detect charged-particle and light radiation emanatingfrom the sample in sequence.
 4. A charged-particle beam microscopeaccording to claim 1, wherein the light beam column further comprises abeam scanner to scan the light beam across the sample.
 5. Acharged-particle beam microscope according to claim 4, wherein the beamscanner comprises microelectromechanical systems (MEMS) or one or morecoil-driven mirrors.
 6. A charged-particle beam microscope according toclaim 1, wherein the controller is adapted to process the detectedcharged-particle radiation to generate a high-resolution grayscale imageand to process the detected light radiation to colorize the grayscaleimage.
 7. A charged-particle beam microscope according to claim 1,wherein the charged-particle beam column is adapted to have a firstfield of view and the light beam column is adapted to have a secondfield of view that is greater than the first field of view.
 8. Acharged-particle beam microscope according to claim 1, wherein the lightbeam column is adapted to converge the light beam to a first beam sizeand the charged-particle beam column is adapted to converge thecharged-particle beam to a second beam size that is smaller than thefirst beam size.
 9. A charged-particle beam microscope for imaging asample, the microscope comprising: a stage to hold a sample; acharged-particle beam column to direct a charged-particle beam onto thesample, the charged-particle beam column comprising: a charged-particlebeam source to generate a charged-particle beam, charged-particle beamoptics to converge the charged-particle beam onto the sample, and afirst detector to detect charged-particle radiation emanating from thesample to generate an image; a light beam column to direct a light beamonto the sample, the light beam column comprising: a light beam sourceto generate a light beam, light-beam optics to converge the light beamonto the sample, a beam scanner to scan the light beam across thesample, and a second detector to detect light emanating from the sampleto generate a second image; and a controller to analyze the detectedcharged-particle radiation and the detected light to generate an imageof the sample.
 10. A charged-particle beam microscope according to claim9, wherein the light beam source is adapted to generate a light beamhaving one or more preselected wavelengths.
 11. A charged-particle beammicroscope according to claim 9, wherein the second detector is adaptedto detect light having one or more preselected wavelengths.
 12. Acharged-particle beam microscope according to claim 11, wherein thesecond detector comprises a color light filter.
 13. A charged-particlebeam microscope according to claim 9, wherein the light beam columncomprises a plurality of second detectors to detect light emanating fromthe sample, each of the second detectors being adapted to detect lighthaving one or more preselected wavelengths.
 14. A charged-particle beammicroscope according to claim 9, wherein the controller is adapted tooperate the charged-particle beam column and the light beam column todetect both charged-particle and light radiation emanating from thesample substantially simultaneously.
 15. A charged-particle beammicroscope according to claim 9, wherein the controller is adapted tooperate the charged-particle beam column and the light beam column todetect charged-particle and light radiation emanating from the sample insequence.
 16. A charged-particle beam microscope according to claim 9,wherein the beam scanner comprises microelectromechanical systems (MEMS)or one or more coil-driven mirrors.
 17. A charged-particle beammicroscope according to claim 9, wherein the controller is adapted toprocess the detected charged-particle radiation to generate ahigh-resolution grayscale image and to process the detected light tocolorize the grayscale image.
 18. A charged-particle beam microscopeaccording to claim 9, wherein the charged-particle beam column isadapted to have a first field of view and the light beam column isadapted to have a second field of view that is greater than the firstfield of view.
 19. A charged-particle beam microscope according to claim9, wherein the charged-particle beam column is adapted to operate at ahigher resolution than the light beam column.
 20. A charged-particlebeam microscope according to claim 9, wherein the light beam sourcecomprises a laser source.